Oscillators having arbitrary frequencies and related systems and methods

ABSTRACT

Systems and methods for operating with oscillators configured to produce an oscillating signal having an arbitrary frequency are described. The frequency of the oscillating signal may be shifted to remove its arbitrary nature by application of multiple tuning signals or values to the oscillator. Alternatively, the arbitrary frequency may be accommodated by adjusting operation one or more components of a circuit receiving the oscillating signal.

RELATED APPLICATIONS

This application claims the benefit as a continuation under 35 U.S.C.§120 of U.S. patent application Ser. No. 12/721,472, filed Mar. 10, 2010under Attorney Docket No. G0766.70015US02 and entitled “OscillatorsHaving Arbitrary Frequencies and Related Systems and Methods”, whichclaims the benefit under 35 U.S.C. §119(e) of U.S. Provisional PatentApplication Ser. No. 61/289,984, filed on Dec. 23, 2009 under AttorneyDocket No. G0766.70015US00 and entitled “Oscillators Having ArbitraryFrequencies and Related Systems and Methods”, both of which applicationsare hereby incorporated herein by reference in their entireties.

BACKGROUND

1. Field

The technology described herein relates to oscillators providingoscillating signals having arbitrary frequencies and to systems andmethods for using the same.

2. Related Art

Oscillators are ubiquitous components in electronic equipment includingwireless and wireline communications systems, entertainment electronics,aerospace systems, and timing systems. The oscillators traditionally areused to provide a reference signal or clock signal, such that precisionof the signal frequency is important. Conventionally, crystaloscillators having quartz crystals as the resonating element have servedas the oscillators of choice because they can be manufactured to provideprecise signal frequencies within ±1.5 parts-per-million (ppm) of atarget frequency value, frequency stabilities of ±2.5 ppm over theentire operating temperature range from −40° C. to +85° C., aging ofbelow ±1 ppm/year (at 25° C.), typical phase noise of −138 dBc/Hz at 1kHz, and power consumption as low as 1.5 mA.

Standard frequencies for reference signals and clock signals havedeveloped, and oscillator manufacturing has conformed to these standardfrequencies. Typical frequency values are as low as 32.768 kHz for watchcrystals and real time clocks. Frequencies in the MHz range are commonlyused in cell phones and GPS receivers, including 12.6 MHz, 13 MHz, 14.4MHz, 16 MHz, 16.368 MHz, 16.9 MHz, 19.2 MHz, 19.8 MHz, 20 MHz, 23.104MHz, 24.554 MHz, 26 MHz, 27.456 MHz, 32 MHz, 33.6 MHz, 38.4 MHz, and 52MHz. Owing to the ability to manufacture quartz crystals to provide aprecise target frequency, it is conventional for crystal oscillators tobe manufactured to provide one of the several standard frequencies.

Thus, circuits and systems including crystal oscillators or receivingsignals from crystal oscillators are conventionally designed to workwith one of the standard frequencies corresponding to the particularcrystal oscillator being used. FIG. 1A illustrates a conventionalapparatus 100 including an oscillator 102 and system 106 that receivesat its input port 105 an oscillator signal 104 output from an outputport 103 of the oscillator 102. The system 106 is designed to work witha signal of precisely 26 MHz. Therefore, a 26 MHz oscillator is selectedfor the oscillator 102. If the system 106 receives a differentfrequency, it will not operate properly.

In some conventional devices, circuitry is designed to operate with afrequency other than that provided by the oscillator, but which can beprecisely generated from a known, precise oscillator frequencyconforming to one of the standard frequencies. Referring to FIG. 1B, theapparatus 150 includes the previously described oscillator 102 and asystem 156, which itself includes a frequency synthesizer 158 and asub-system 162. The sub-system 162 is designed to operate with afrequency other than the 26 MHz of oscillator signal 104 provided by theoscillator 102. The frequency synthesizer receives the oscillator signal104 at its input port 155 and generates a synthesized signal 160, whichcan be referred to as an internal signal since it is generated and usedinternally to system 156, having the frequency required by sub-system162. If the synthesizer 158 does not receive a precise 26 MHz signalfrom the oscillator, it will not generate the precise frequency requiredby subsystem 162, and therefore the subsystem 162 will not operateproperly.

In the event that an oscillator does not provide a frequency preciselymatching that required by a system, some conventional devices includecircuitry to provide a tuning signal to the oscillator, referred to asautomatic frequency control (AFC), as shown in FIGS. 2A and 2B. Theapparatus 200 of FIG. 2A includes a 26 MHz oscillator 202 which providesthe oscillator signal 104 to a system 206. Although the oscillator 202is shown as a 26 MHz oscillator, for conventional oscillators theoscillator signal 104 can differ from 26 MHz by ±2 ppm. The system 206determines whether the oscillator signal 104 has a frequency ofprecisely 26 MHz, and includes an output port 208 from which is providedan AFC tuning signal 210 to tune the oscillator if the oscillator signal104 is not precisely 26 MHz. The AFC tuning signal 210 is received at anelectronic frequency control input port (EFC_tune) 204 of theoscillator.

In FIG. 2B, the apparatus 250 includes the 26 MHz oscillator 202 and asystem 256 having an input terminal 255 to receive the oscillator signal104. The frequency synthesizer 258 generates a synthesized, or internal,signal 212 which is provided to the subsystem 262. The subsystem 262detects whether the synthesized signal has the precise frequencyrequired for proper operation of the sub-system and provides, via outputport 264, the AFC tuning signal 210 to tune the oscillator 202 if thefrequency of synthesized signal 212 does not precisely match therequired frequency.

Conventional AFC tuning is limited to ±30 ppm of an initial frequency bythe properties of the quartz crystals used as the resonating elements ofconventional crystal oscillators, and is typically limited to ±10 ppm inpractice.

SUMMARY

According to one aspect of the present invention, a method of generatingan oscillating signal having a target frequency from an oscillatorhaving a mechanical resonator is provided, the oscillator being coupledto a circuit to provide the oscillating signal to the circuit. Themethod comprises applying to the oscillator, from the circuit, a firsttuning signal having a first value, and applying to the oscillator, fromthe circuit, an automatic frequency control (AFC) tuning signal having asecond value different than the first value.

According to another aspect of the present invention, an apparatus isprovided comprising an oscillator having a mechanical resonator, atleast one input port, and at least one output port, the oscillator beingconfigured to provide an oscillating output signal at the at least oneoutput port. The apparatus further comprises a circuit having at leastone input port coupled to the at least one output port of the oscillatorto receive the oscillating output signal, and further having at leastone output port coupled to the at least one input port of theoscillator. The circuit is configured to provide at its at least oneoutput port at least one tuning signal for tuning the oscillator, the atleast one tuning signal comprising an automatic frequency control (AFC)tuning signal and at least one additional tuning signal.

According to another aspect of the present invention, an apparatus isprovided comprising an oscillator comprising a mechanical resonator anda memory storing at least one value indicative of a frequency of theoscillator and/or of the mechanical resonator.

According to another aspect of the present invention, a method isprovided, comprising outputting, from an oscillator comprising amechanical resonator to a circuit coupled to the oscillator, at leastone value indicative of a frequency of the oscillator and/or of themechanical resonator.

According to another aspect of the present invention, a method isprovided, comprising downconverting a cellular telephone signal, thecellular telephone signal modulated with data, using an oscillatingreference signal having an arbitrary frequency to generate adownconverted signal including the data. The method further comprisessampling the downconverted signal with an analog-to-digital converter(ADC) using a sampling rate selected to induce a shift of the data ofthe downconverted signal in a frequency domain.

According to another aspect of the present invention, a method isprovided, comprising generating a digital data signal having digitaldata, and sampling the digital data signal with a digital-to-analogconverter (DAC) using a sampling rate selected to induce a shift of thedigital data in a frequency domain, the sampling resulting in an analogsignal. The method further comprises upconverting the analog signalusing an oscillating reference signal having an arbitrary frequency togenerate an upconverted signal including data corresponding to thedigital data.

According to another aspect of the present invention, a method isprovided, comprising downconverting a first signal, the first signalmodulated with data, using an oscillating reference signal having anarbitrary frequency to generate a downconverted signal including thedata. The method further comprises sampling the downconverted signalwith an analog-to-digital converter (ADC) to produce a digital signalincluding digital data corresponding to the data. The method furthercomprises shifting, using a digital signal processor (DSP), the digitaldata in a frequency domain.

According to another aspect of the present invention, a method isprovided, comprising generating a digital data signal having digitaldata, and shifting the digital data in a frequency domain using adigital signal processor (DSP). The method further comprises samplingthe shifted digital data with a digital-to-analog converter (DAC) toproduce an analog signal, and upconverting the analog signal using anoscillating reference signal having an arbitrary frequency to generatean upconverted signal including data corresponding to the digital data.Shifting the digital data in the frequency domain comprises shifting thedigital data by a frequency amount selected to account for a deviationof the arbitrary frequency from a standard oscillator frequency.

According to another aspect of the present invention, a method isprovided, comprising downconverting a first signal, the first signalmodulated with analog data, using an oscillating reference signal havingan arbitrary frequency to generate a downconverted signal including theanalog data, the arbitrary frequency differing from a standardoscillator frequency. The method further comprises sampling thedownconverted signal with an analog-to-digital converter (ADC) toproduce a digital signal including digital data corresponding to theanalog data. The sampling is performed using a sampling ratecorresponding to the standard oscillator frequency. The method furthercomprises applying the digital signal to a carrier tracking loop.

BRIEF DESCRIPTION OF THE DRAWINGS

Description of various aspects and embodiments of the invention will begiven by reference to the following drawings. The drawings are notnecessarily drawn to scale. Each identical or nearly identical componentillustrated in multiple drawings is illustrated by a like numeral.

FIG. 1A illustrates a conventional configuration of an oscillatorproviding to a system an oscillating signal having a standard frequency.

FIG. 1B illustrates a detailed view of a conventional system forgenerating an internal signal from an oscillating signal of standardfrequency received from an oscillator.

FIG. 2A illustrates a conventional configuration of an oscillatorproviding an oscillating signal to a system and the system applying anautomatic frequency control (AFC) signal to the oscillator.

FIG. 2B illustrates a conventional configuration of an oscillatorproviding an oscillating signal to a system which generates an internalsignal, and in which the system applies an AFC signal to the oscillator.

FIG. 3 illustrates in block diagram form an apparatus comprising asystem coupled to an oscillator configured to generate an oscillatingsignal having an arbitrary frequency, according to one embodiment of thepresent invention.

FIG. 4 illustrates in block diagram form an apparatus comprising asystem coupled to an oscillator configured to generate an oscillatingsignal having an arbitrary frequency and in which the system generatesan internal signal from the oscillating signal, according to analternative embodiment of the present invention.

FIG. 5 illustrates a radio frequency (RF) front-end employing anoscillator configured to generate an oscillating signal having anarbitrary frequency, according to one embodiment of the presentinvention.

FIG. 6 illustrates an alternative RF front-end employing an oscillatorconfigured to generate an oscillating signal having an arbitraryfrequency, and in which an analog-to-digital converter is configured tooperate as a mixer, according to another embodiment of the presentinvention.

FIG. 7 illustrates an alternative RF front-end employing an oscillatorconfigured to generate an oscillating signal having an arbitraryfrequency, and in which a digital signal processor (DSP) is configuredto induce a frequency shift of digital data, according to anotherembodiment of the present invention.

FIG. 8 illustrates an RF front-end including a carrier tracking loop andemploying an oscillator configured to generate an oscillating signalhaving an arbitrary frequency, according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

While, as described above, conventional quartz crystal resonators can bemanufactured to provide an oscillating signal of precise frequency,doing so requires significant effort and cost. Accordingly, Applicantshave appreciated that the effort and cost associated with manufacturingconventional quartz crystal resonators may be minimized or eliminated bydesigning systems which may accurately operate in combination with anoscillator manufactured to produce an arbitrary frequency rather than aconventionally accepted (standard) oscillator frequency. As used herein,“arbitrary frequency” refers to a frequency not substantially matching aconventional standard oscillator frequency. For example, the arbitraryfrequency may differ by at least 30 parts per million (ppm) from astandard oscillator frequency in some embodiments. In some embodiments,the arbitrary frequency may differ by at least 50 ppm from a standardoscillator frequency, by at least 100 ppm, by at least 200 ppm, by atleast 500 ppm, by at least 1,000 ppm, or by between approximately 1,000ppm and 10,000 ppm (e.g., 2,000 ppm, 5,000 ppm, or any other valuewithin this range), among other possible amounts of deviation. The term“arbitrary frequency” as used herein does not imply the frequency is notknown or cannot be measured. Rather, an arbitrary frequency may bemeasured or otherwise have its value determined.

Furthermore, systems as described herein which may accurately operate incombination with an oscillator manufactured to produce an oscillatingsignal of arbitrary frequency may enable the use of mechanical resonatortechnologies which cannot be manufactured with the precision ofconventional quartz crystal resonators, but which may offer variousadvantages over quartz crystal resonator technology. For example,oscillators employing MEMS resonator technology may not be easilymanufactured to conform to one of the standard oscillator frequencies,but rather may be manufactured with less precision to provide anarbitrary frequency, thus making them less desirable than quartz crystalresonators for many present day applications in which a frequencyprecisely matching a conventional standard oscillator frequency isrequired. However, oscillators employing MEMS resonator technology mayoffer benefits compared to conventional quartz crystal resonators interms of, for example, frequency stability, ease of manufacturing,manufacturing compatibility of the materials of the oscillator and/ormechanical resonator, cost, or other beneficial characteristics.Accordingly, it may be desirable to use oscillators employing MEMSresonator technology for some applications. One or more of the aspectsof the invention described herein may enable or facilitate use of suchtechnologies.

Accordingly, aspects of the present invention provide oscillatorsconfigured to produce oscillating signals having arbitrary frequenciesand related systems and methods which may properly operate in connectionwith such oscillators. For purposes of the following discussion, thedescribed systems and methods may be grouped into one of two classes,although it should be appreciated that the classes are not necessarilymutually exclusive and may overlap in one or more embodiments. The firstclass includes systems and methods which generate, from an oscillatorconfigured to produce an oscillating signal of arbitrary frequency orfrom the oscillating signal of arbitrary frequency, an oscillatingsignal having a standard oscillator frequency. For example, thearbitrary frequency may differ from a standard oscillator frequency(e.g., 26 MHz) by up to ±10,000 ppm or more, and the systems and methodsaccording to the first class discussed herein may generate from theoscillator or the oscillating signal of arbitrary frequency a signalhaving the standard frequency. A second class of systems and methodsdescribed herein are those which operate with a received oscillatorsignal of arbitrary frequency and do not shift the oscillator signal toa standard frequency, but rather adapt the configuration and/oroperation of one or more components of the system to account for thearbitrary frequency.

Thus, according to one aspect of the present invention, a method ofgenerating an oscillating signal having a target frequency (e.g., astandard oscillator frequency) from an oscillator having a mechanicalresonator and configured to provide an arbitrary frequency is provided.A first tuning signal may be applied to the oscillator to shift afrequency of the oscillating signal produced by the oscillator. Themethod may further involve applying an automatic frequency control (AFC)tuning signal to the oscillator. The first tuning signal and the AFCtuning signal may have different values, and may form distinct signalsin some embodiments. In alternative embodiments, the first tuning signaland the AFC tuning signal may form different components of a singlesignal. As will be described further below, the first tuning signal mayinfluence a larger frequency shift of the oscillating signal output bythe oscillator than the AFC tuning signal. Thus, the first tuning signalmay be thought of as a coarse tuning signal, while the AFC tuning signalmay operate as a fine tuning signal in some embodiments.

According to another aspect of the present invention, a circuit orsystem coupled to an oscillator and configured to receive an oscillatingsignal from the oscillator is configured to apply multiple tuningsignals to the oscillator to control a frequency of the oscillatingsignal output by the oscillator. The oscillator may include a mechanicalresonator of any suitable resonating technology, including MEMStechnology, quartz crystal resonator technology, or any other suitablemechanical resonating technology. According to some embodiments, thecircuit or system is configured to apply two tuning signals to theoscillator. One of the tuning signals may correspond to an AFC tuningsignal, and the other tuning signal may be distinct from the AFC tuningsignal and may represent a “frequency steering” signal, as describedfurther below. The tuning signals may be provided separately, or in someembodiments may be provided as different components of a same signal.The value of the AFC tuning signal may influence a relatively smallfrequency shift of the oscillating signal output by the oscillator,whereas the additional frequency steering tuning value may influence arelatively larger frequency shift of the oscillating signal. The valuesof the AFC tuning signal and the additional tuning signal may beselected to shift the frequency of the oscillating signal output by theoscillator from an arbitrary frequency to a desired standard oscillatorfrequency.

According to some embodiments of the above-described aspects of thepresent invention, the values of one or both of the tuning signals maybe determined at least in part based on the arbitrary frequency of theoscillating signal output by the oscillator. The value of the arbitraryfrequency may be determined in various suitable manners, and may beprovided to the appropriate circuitry within the oscillator and/orcircuit or system operating in connection with the oscillator in anysuitable manner. According to one aspect of the present invention, anoscillator including a mechanical resonator also includes memory storinga value indicative of a frequency of the oscillator and/or themechanical resonator. The value stored in memory of the oscillator andindicative of the frequency of the oscillator and/or mechanicalresonator may be provided to a circuit or system operating in connectionwith the oscillator, for example in addition to the oscillating outputsignal itself. Thus, according to one aspect of the present invention,an oscillator outputs an oscillating output signal having an arbitraryfrequency as well as value indicative of the arbitrary frequency.

As mentioned, a second class of systems and methods according to thevarious aspects of the invention described herein are those whichoperate with a received oscillator signal of arbitrary frequency and donot shift the oscillator signal to a standard oscillator frequency, butrather adapt the configuration and/or operation of one or morecomponents of the system to account for the arbitrary frequency.According to one such aspect of the present invention, a method isprovided for operating on a cellular telephone signal using anoscillating reference signal having an arbitrary frequency. The cellulartelephone signal may be down-converted to an intermediate frequencyusing the oscillating reference signal of arbitrary frequency, resultingin a down-converted signal including data corresponding to the data ofthe cellular telephone signal. As a result of performing thedown-conversion with an oscillating reference signal of arbitraryfrequency, the data of the down-converted signal may be shifted in thefrequency domain relative to the intermediate frequency. Thedown-converted signal may then be sampled with an analog-to-digitalconverter (ADC). The sampling rate of the ADC may be selected to inducea shift in the frequency domain of the data of the down-converted signalto compensate for the shift of the data of the down-converted signalfrom the intermediate frequency.

According to another such aspect of the invention, the sampling rate ofa digital-to-analog converter (DAC) in a transmit path of a device, suchas a cellular telephone or other transmission device, may be selected toaccount for an up-conversion process performed in the transmit pathusing an oscillating reference signal having an arbitrary frequency. Theup-conversion process may be performed by suitable mixing of an analogsignal including analog data, such as a cellular telephone signal orother analog signal to be transmitted, with an oscillating referencesignal, resulting in an up-converted signal at a desired carrierfrequency. The analog signal itself may be generated by performingdigital-to-analog conversion of a digital signal having the desired datafor transmission. The transmit path may be designed to operate with anoscillating reference signal having a standard oscillator frequency,such that if the oscillating reference signal instead has an arbitraryfrequency the data of the resulting up-converted signal may be shiftedin the frequency domain relative to the center frequency of the desiredcarrier frequency. Such a shift may be accounted for by suitableselection of the sampling rate of the DAC prior to up-conversion, suchthat the data of the up-converted signal appears at the intermediatefrequency. For example, if the arbitrary frequency of the oscillatingreference signal is higher than an expected standard oscillatorfrequency, then the sampling rate of the DAC may be selected to be lowerthan if the oscillating reference signal had the expected standardoscillator frequency, and vice versa.

According to another such aspect of the present invention, a method ofaccounting for down-conversion of a received signal using an oscillatingreference signal of arbitrary frequency may comprise using a digitalsignal processor (DSP) to digitally shift the data of the down-convertedsignal in the frequency domain. A carrier signal modulated with data maybe received and down-converted using the oscillating reference signal ofarbitrary frequency, thus resulting in a down-converted signal includingdata corresponding to the data modulated on the carrier signal. Thedown-converted signal may then be sampled using an ADC to produce adigital signal including digital data corresponding to the datamodulated on the carrier signal. Because the down-conversion of thecarrier signal is performed using an oscillating reference signal havingan arbitrary frequency, the digital data of the resulting down-convertedand digitized signal may be shifted in the frequency domain relative tothe baseband frequency and/or intermediate frequency. Accordingly, thedigitized signal output by the ADC may be provided to a DSP, which maydigitally shift the data of the digitized signal in the frequencydomain.

According to another such aspect of the present invention, a digitalshift of data to be transmitted from a transmit path of a device, suchas a cellular telephone or other transmission device, may be induced toaccount for an up-conversion process performed using a referenceoscillating signal having an arbitrary frequency. A digital data signalhaving digital data to be transmitted may be generated. The digital datasignal may be digital-to-analog converted using a DAC and thenup-converted by mixing with a suitable oscillating reference signal. Thedevice may be designed in expectation of the oscillating referencesignal having a standard oscillator frequency. In the event theoscillating reference signal has an arbitrary frequency, theup-conversion process may result in the data to be transmitted beingshifted in the frequency domain relative to the center frequency of theintended carrier frequency. To account for such a shift, a digitalsignal processor (DSP) may be used to shift, in the frequency domain,the digital data of the digital data signal prior to thedigital-to-analog conversion. By suitable selection of the amount offrequency shift to induce in the digital data signal, the subsequent DACconversion and up-conversion using an oscillating reference signal ofarbitrary frequency may result in the data of the up-converted signalappearing at a desired frequency or frequencies (e.g., near the centerfrequency of the desired carrier frequency).

According to a further such aspect of the present invention, a method ofoperating on a signal down-converted using an oscillating referencesignal having an arbitrary frequency comprises utilizing a carriertracking loop. A carrier signal modulated with data may be received anddown-converted using the oscillating reference signal of arbitraryfrequency, resulting in a down-converted signal. The down-convertedsignal may then be sampled with an ADC, producing a digital signalincluding digital data corresponding to the data modulated on thecarrier signal. The sampling rate of the ADC may be selected as if theoscillating reference signal had a standard oscillator frequency and notan arbitrary frequency. For example, the sampling rate of the ADC may beselected as if the oscillating reference signal had a standardoscillator frequency of, for example, 26 MHz, rather than an arbitraryfrequency differing from the standard operating frequency by up toapproximately ±10,000 ppm. As a result, the digitized signal may includedigital data not accurately reflecting the data modulated on the carriersignal. The digitized signal may be applied to a carrier tracking loop,thus effectively re-sampling the digital data of the digital signal torestore its accuracy.

The various aspects described above, as well as further aspects, willnow be described in further detail below. It should be appreciated thatthese aspects may be used alone, all together, or in any combination oftwo or more, to the extent that they are not mutually exclusive. Also,while various of the aspects will be described below in the context ofcellular telephone systems, it should be appreciated that the aspectsare not limited in this respect, and may apply to other devices andsystems which use a reference oscillator, such as navigation receivers(e.g., global positioning system (GPS) receivers), personal digitalassistants (PDAs), other wireless communication devices, timingcircuits, or other devices using reference oscillators.

As mentioned, according to one class of systems and methods describedherein, an oscillating signal having a standard oscillator frequency isgenerated from an oscillator configured to produce an oscillating signalof arbitrary frequency. One non-limiting example of a system and methodfor doing so is to provide multiple tuning signals (which may involve,in some instances, providing multiple tuning values) to the oscillator.An example of an apparatus according to this aspect of the presentinvention is illustrated in FIG. 3.

As shown, the apparatus 300 includes an oscillator 302 and a system 306.According to one embodiment, the oscillator and system may be formed onseparate semiconductor dies (which may facilitate separate manufactureof the two), although not all embodiments are limited in this respect.The oscillator 302 is configured to provide from an output port 303 anoscillating output signal 304. The oscillating output signal 304 isreceived by an input port 305 of the system 306. As shown, theoscillator 302 may be configured (e.g., by its manufacture) to produce asignal of, as a non-limiting example, 25.97425 MHz, or in other words anarbitrary frequency. The system 306 may be configured to operate with aprecise standard oscillator frequency, such as, for example, 26 MHz,such that the 25.97425 MHz which oscillator 302 is configured to produceis not suitable for proper operation of the system 306. Accordingly, towork with the oscillator 302, the system 306 may be configured toprovide two tuning signals to the oscillator 302 to influence thefrequency of the oscillating output signal 304, and in some embodimentsto control the frequency of the oscillating output signal 304 to have itmatch a standard oscillator frequency.

As shown, a first tuning signal 308 is provided from a first output port310 of the system 306 to a first input port 312 of the oscillator 302.An AFC tuning signal 314 is also provided from an output port 316 of thesystem 306 to a second input port 318 of the oscillator 302. As will bedescribed further below, the values of the tuning signal 308 and the AFCtuning signal 314 may be selected to tune the oscillator 302 such thatthe oscillating output signal 304 has a standard oscillator frequencyrather than the arbitrary frequency which oscillator 302 is configuredto produce, or so that the oscillating output signal has a frequencyenabling the system 306 itself to generate from the oscillating outputsignal 304 an oscillating signal (e.g., an internal signal) having adesired standard oscillator frequency.

According to one embodiment, a combination of tuning signal 308 and AFCtuning signal 314 may induce a frequency shift of up to approximately±10,000 ppm (e.g., up to approximately ±500 ppm, ±1,000 ppm, ±2,000 ppm,±5,000 ppm, or any other suitable amount) of the oscillating outputsignal 304, or any other suitable amount. Thus, a large frequency shiftof the oscillating output signal 304 may be realized by use of tuningsignals 308 and 314, enabling or facilitating use of an oscillator 302configured to produce an arbitrary frequency with the system 306.According to one embodiment, the value of tuning signal 308 induces arelatively larger frequency shift of the oscillating output signal 304than does the AFC tuning signal 314. Thus, the tuning signal 308 may bethought of as a coarse adjustment tuning signal, and is referred toherein as a “frequency steering” signal (which is why output port 310 islabeled “FS” and input port 312 is labeled “FS_tune”), while the AFCtuning signal may be thought of as a fine adjustment tuning signal.According to one embodiment, the AFC tuning signal induces a relativelysmall frequency shift of the oscillating output signal 304 of, forexample, less than approximately ±5 ppm, less than approximately ±10ppm, or less than approximately ±20 ppm, as a continuous value or inincrements of any suitable size. Thus, it should be appreciated that thetuning signal 308 may induce a substantially larger frequency shift, forexample, up to approximately ±10,000 ppm according to some embodiments.The tuning signal 308 may induce a frequency shift of certain distinctvalues in increments of ±50 ppm, ±100 ppm, ±200 ppm, or any othersuitable amount.

The form of tuning signals 308 and 314, and the manner and timing inwhich they are provided to the oscillator 302, are not limiting.According to one embodiment, the form of tuning signal 308 may depend ona type of tuning technique used to tune oscillator 302. For example,according to one embodiment the oscillator 302 may be tunable byinducing a phase shift between an output signal of the oscillator and aninput signal of the oscillator, for example if the oscillator comprisesor is part of a feedback loop. An example of such a device with whichthe aspects described herein may be applied is described in co-pendingU.S. patent application Ser. No. 12/699,094, filed Feb. 8, 2010 underAttorney Docket No. G0766.70007US02, entitled “Methods and Apparatus forTuning Devices Having Mechanical Resonators”, which application ishereby incorporated herein by reference in its entirety. In such anembodiment, the tuning signal 308 may be any signal suitable forselecting or inducing a desired amount of phase shift. According toanother embodiment, the oscillator 302 may be tunable by inducing aphase shift and an amplitude shift between an output signal of theoscillator and an input signal to the oscillator, for example again ifthe oscillator comprises or forms part of a feedback loop. Examples ofsuch devices are also described in U.S. patent application Ser. No.12/699,094. In such a non-limiting embodiment, tuning signal 308 may beany signal suitable for selecting or inducing a desired amount of phaseshift and/or amplitude adjustment. Other tuning techniques for tuningthe oscillator 302 are also possible, and tuning signal 308 may take anysuitable form for dictating or selecting the amount of frequency shiftby which to shift the frequency of the oscillating output signalprovided by the oscillator.

According to one embodiment, the value of tuning signal 308 may be adigital value which may effectively program the oscillator 302, thusinducing a frequency shift of the oscillating output signal 304. Forexample, in one embodiment the oscillator 302 may be tunable by inducinga phase shift between an output signal and input signal of theoscillator, and the tuning signal may be a digital value indicating anamount of phase shift to induce. According to one such embodiment, thetuning signal 308 may be a digital code, which may be decoded (e.g., bysuitable decoding circuitry of the oscillator) to determine an amount ofphase shift to induce. It should be appreciated that digital codes maysimilarly be used with oscillators tuned by different tuning techniques(e.g., other than by inducing a phase shift between input and outputsignals of the oscillator).

The tuning signal 308 may be provided once (e.g., upon powering on ofthe system 306) to the oscillator 302, at periodic intervals, when adevice of which apparatus 300 forms a part changes a frequency ofoperation (e.g., when a cell phone changes frequency channels),substantially continuously, or at any other suitable time. According toan alternative embodiment, the tuning signal 308 may be an analog tuningvoltage applied at any of the above-described times or any othersuitable time. According to one embodiment, the value of the frequencysteering signal may be stored in local memory of the oscillator uponreceipt from the system.

The AFC tuning signal 314 provided to input port 318 (labeled as“EFC_tune”) may be substantially the same as a conventional AFC tuningsignal, and therefore may be either an analog tuning voltage or adigital signal, as the various aspects described herein implementing anAFC tuning signal are not limited to the form of the tuning signalunless otherwise stated. The AFC tuning signal 314 may be appliedcontinuously to the system 302, for example as an analog tuning voltage,and may vary regularly to account for relatively small deviations of thefrequency of oscillating output signal 304 from a target frequency.Other forms and timing of application are also possible for AFC tuningsignal 314.

As mentioned, the manner in which the tuning signals 308 and 314 areprovided to oscillator 302 is also not limiting. According to oneembodiment, as shown in FIG. 3, tuning signals 308 and 314 may beprovided as distinct signals to the oscillator (e.g., on separate wireleads or signal traces). According to another embodiment, tuning signals308 and 314 may be provided as a single signal (e.g., on a single wirelead or signal trace) to the oscillator. In such an embodiment, thetuning signals 308 and 314 may represent different components orportions of a single tuning signal. Thus, it should be appreciated thatthe form and manner of applying tuning signals 308 and 314 to theoscillator are not limiting.

While the oscillator 302 is not limited to utilizing any particular typeof mechanical resonator technology, and therefore may utilizeconventional quartz crystal resonator technology, MEMS resonatortechnology, or any other suitable technology, it should be appreciatedthat the amount of frequency shift which may be induced by thecombination of tuning signal 308 and AFC tuning signal 314 may belimited at least in part by the type of resonator technology employed.For example, conventional quartz crystal resonator technology may notallow for tuning up to approximately ±10,000 ppm of the initialoscillator output signal frequency. Thus, it should be appreciated thatthose embodiments described herein relating to tuning of an oscillatoroutput signal frequency by up to approximately ±10,000 ppm maycorrespond to embodiments in which the oscillator employs mechanicalresonator technology allowing for such a relatively large tuning range.According to one embodiment, MEMS resonator technology, such as thatdescribed in U.S. patent application Ser. No. 12/181,531, filed Jul. 29,2008 under Attorney Docket No. G0766.70004US00, entitled“Micromechanical Resonating Devices and Related Methods” and publishedas U.S. Patent Application Publication No. 2010-0026136-A1, and U.S.patent application Ser. No. 12/142,254, filed Jun. 19, 2008 underAttorney Docket No. G0766.70003US01, entitled “Methods and Devices ForCompensating a Signal Using Resonators” and published as U.S. PatentApplication Publication No. 2009-0243747-A1, may be employed, both ofwhich applications are hereby incorporated herein by reference in theirentireties.

The system 306 may include any suitable circuitry for providing thetuning signals 308 and 314, and may include any suitable circuitry fordetermining the values of those signals. According to one aspect of thepresent invention, the system 306 may determine suitable values fortuning signals 308 and 314 by comparison of the frequency of theoscillating output signal 304 to a reference frequency, such as a radiofrequency signal of known frequency received by a device of whichapparatus 300 forms a part (e.g., a cellular telephone). For example,according to one embodiment, the system 306 receives the oscillatingoutput signal 304 having the initially arbitrary frequency and comparesthe received oscillating signal to a reference signal having a knownfrequency, which may correspond to a target frequency. If the system 306determines that the oscillating output signal 304 does not have thedesired target frequency, the frequency difference between that of theoscillating output signal 304 and the target frequency may bedetermined, and suitable values for the tuning signals 308 and 314 toadjust the arbitrary frequency of oscillating output signal 304 to thedesired target frequency may be determined.

According to another embodiment, the frequency of the output signalprovided by the oscillator may be directly measured, for example using afrequency analyzer or any other suitable technique. Such measurement maybe made after manufacture of the oscillator or at any other suitabletime. The measured frequency may be compared to a target value, fromwhich suitable values for tuning signals 308 and 314 to adjust thearbitrary frequency of oscillating output signal 304 to the desiredtarget frequency may be determined.

According to another embodiment, the values of one or both of tuningsignals 308 and 314 may be determined based on a known value of thearbitrary frequency of oscillator 302. For example, as shown in FIG. 3,according to one embodiment the oscillator 302 provides from memory 313a value 320 indicative of the arbitrary frequency, which may be receivedat an input port 315 of the system 306 (labeled as port “f_zero” sincethe initial arbitrary frequency of the oscillator may be labeled“f_zero”). Value 320 may be one of various values which the system 306may use to determine appropriate values for tuning signals 308 and 314.For example, according to one embodiment, value 320 is a value of thefrequency of oscillator 302 (e.g., 25.97425 MHz), for example, thearbitrary frequency. According to an alternative embodiment, value 320is a value of an offset of the arbitrary frequency from a standardfrequency. For example, value 320 may be 5,000 if the arbitraryfrequency differs from a standard oscillator frequency of known value by5,000 ppm. According to a further embodiment, value 320 may be a valueof a frequency of the mechanical resonator of oscillator 302 (e.g.,25.99955 MHz), which may be indicative of the arbitrary frequency ofoscillating output signal 304. According to another alternativeembodiment, the value 320 may be a value of an offset of the frequencyof the mechanical resonator of oscillator 302 from a standard oscillatorfrequency (e.g., value 320 may be 1,000 if the frequency of themechanical resonator differs by 1,000 ppm from a standard oscillatorfrequency). Other values are also possible, as the value 320 is notlimited to representing any specific physical quantity, but rather mayrepresent one of various quantities which the system 306 maysatisfactorily use to determine appropriate values for tuning signals308 and/or 314.

Memory 313 storing the value 320 may be any suitable type of memory.According to one embodiment, the value 320 may be provided once uponconnection of the system 306 to the oscillator 302. According to analternative embodiment, the value 320 may be provided periodically tothe system 306, for example whenever a device of which apparatus forms apart changes an operating frequency (e.g., when a cellular telephonechanges frequency channels). According to a further embodiment, thevalue 320 may be provided upon powering on of the apparatus 300. Thus,it should be appreciated that the various aspects described hereinrelating to an oscillator including memory providing a value indicativeof a frequency of the oscillator and/or mechanical resonator of theoscillator are not limited to the time or manner in which the value isprovided.

The system 306 may utilize the value 320 in any suitable manner fordetermining suitable values of tuning signals 308 and 314. According toone embodiment, system 306 includes a reference table, such as a lookuptable, storing values for tuning signal 308 based on the arbitraryfrequency of the oscillator 302, an offset of the arbitrary frequencyfrom a standard oscillator frequency, or any other value which may berepresented by value 320, and the desired target frequency of theoscillating output signal 304 (e.g., a desired standard oscillatorfrequency). Thus, according to one embodiment, the system 306 receivesthe value 320 and refers to the reference table/lookup table storedtherein to determine an appropriate value for tuning signal 308 toensure the oscillating output signal 304 has the desired targetfrequency. According to one embodiment, the reference table/lookup tablemay provide values for both tuning signal 308 and tuning signal 314,although not all embodiments are limited in this respect. The referencetable/lookup table within system 306 may be stored within memory ofsystem 306, or in any other suitable manner. Furthermore, the referencetable/lookup table may be populated or uploaded to the system 306 at anysuitable time. For example, the table may be provided to the system 306upon initial manufacturing of the system 306. Alternatively, the tablemay be updated or uploaded to the system 306 periodically.

While FIG. 3 illustrates a non-limiting embodiment in which a value 320is provided from memory 313 to the system 306, it should be appreciatedthat alternative manners for providing the system 306 with suchinformation are possible. For example, according to one alternativeembodiment, the value 320 may be programmed into system 306 uponmanufacture of the system 306, rather than being provided by theoscillator 302. For example, a manufacturer of system 306 may know thevalue 320 prior to oscillator 302 being connected to system 306, andtherefore may provide the value 320 by programming it into memory ofsystem 306, or by providing a lookup table as previously described basedon the known value. According to one embodiment, the value 320 may beprinted on a package of the oscillator 302, and the manufacturer or userof system 306 may read the value from the package and provide it tosystem 306 in any suitable manner. Other alternatives are also possible.

As described above in connection with FIGS. 1B and 2B, some systemsreceive a signal from an oscillator and synthesize an internal signalhaving a different desired frequency. The concepts described withrespect to FIG. 3 may also apply to such a system. An example isillustrated in FIG. 4.

As shown, the apparatus 400 includes the oscillator 302 coupled to asystem 406, which in one embodiment may represent a non-limitingdetailed version of system 306 of FIG. 3. According to one embodiment,the oscillator 302 and system 406 may be formed on separatesemiconductor dies (which may facilitate separate manufacture of thetwo), although not all embodiments are limited in this respect. Thesystem 406 includes a frequency synthesizer 401 having an input coupledto the input port 305 of system 406. Furthermore, the system 406includes a subsystem 402 which receives an output of the frequencysynthesizer 401. In the non-limiting example of FIG. 4, the frequencysynthesizer receives the oscillating output signal 304 of oscillator 302and synthesizes a synthesized (internal) signal 404 which it provides tothe subsystem 402. In some non-limiting embodiments, the frequencysynthesizer may be an integer phase locked loop (PLL) and may be presetto a fixed divider ratio NIR, where N and R are integer numbers, so thatthe resulting frequency output by the frequency synthesizer is relatedto the received frequency (e.g., the frequency of oscillating outputsignal 304) by the ratio NIR. In such a scenario, because the oscillatoroutput signal 304 may have an arbitrary frequency, at least initially,the synthesized signal 404 may also differ from a desired targetfrequency for the internal signal being provided to subsystem 402. Itshould be understood that using an integer phase locked loop is only onepossible embodiment for the frequency synthesizer, and any otherfrequency synthesizer can be used, including fractional N PLL, directdigital synthesizer (DDS), and any other method.

In those scenarios in which the frequency synthesizer is unable togenerate an internal signal having a desired target frequency, forexample because the frequency synthesizer is an integer PLL and theoscillating output signal 304 has an arbitrary frequency, tuning signals308 and 314 may be applied by system 406 to the oscillator 302 to shiftthe frequency of oscillating output signal 304 to a value such thatfrequency synthesizer 401 may then synthesize a synthesized signal 404having a desired target frequency for subsystem 402. Thus, it should beappreciated that tuning signals 308 and 314 in this non-limitingembodiment may not be used to shift the frequency of oscillating outputsignal 304 itself to a standard oscillator frequency (although they mayin some embodiments), but rather to a frequency from which the frequencysynthesizer may generate an internal oscillating signal having thedesired target frequency for sub-system 402.

A non-limiting example is now given. According to one embodiment, thefrequency synthesizer 401 is a PLL having discrete frequency steps of100 ppm. The oscillator 302 may initially output an oscillating outputsignal 304 having the indicated arbitrary frequency of 25.97425 MHz. Dueto the step sizes of the frequency synthesizer 401, the synthesizedsignal 404 may have a frequency that is at best within ±50 ppm of adesired target frequency for the sub-system 402. The tuning signal 308may, in this non-limiting example, have a value that may be selected inincrements of ±10 ppm, and therefore may be selected to have a suitablevalue for adjusting the frequency of oscillating output signal 304 suchthat the synthesized signal 404 has a frequency within ±10 ppm of adesired target frequency for sub-system 402. The AFC tuning signal 314may then assume a value suitable for shifting the frequency of theoscillating output signal 304 by a suitable amount such that frequencysynthesizer 401 may synthesize a synthesized signal 404 having thetarget frequency. It should be appreciated that this is merely onenon-limiting example, and that other manners of operation of theapparatus 400 are also possible. The values of tuning signals 308 and314 in system 406 may be determined in any of the manners describedabove with respect to FIG. 3, or in any other suitable manner.

The techniques described above in connection with FIGS. 3 and 4 may beapplied to various applications and contexts utilizing referenceoscillators to generate an oscillating reference signal. Onenon-limiting example of a system in which a reference oscillator isused, and in which the concepts of FIGS. 3 and 4 may be used, is a radiofrequency (RF) device, such as a cellular telephone. A non-limitingexample is described with respect to FIG. 5, although it should beappreciated that other devices may also utilize the techniques describedherein.

FIG. 5 illustrates an RF front-end 500, as might be used in a cellulartelephone, illustrating in detail the receive path and excluding thedetails of the transmit path 522 for simplicity of the figure. It shouldbe appreciated, however, that the principles of operation described withrespect to the receive path may be analogously applied to the transmitpath, and thus that the various aspects described herein relating to RFfront-ends are not limited to receive paths only.

The RF front-end 500 has a direct-conversion receiver (DCR)architecture, also referred to as a Homodyne, Synchrodyne or zero-IFreceiver. However, it should be appreciated that the aspects describedherein relating to RF front-ends are not limited to the exactconfiguration of components illustrated in FIG. 5 or to any particulartype of RF front-end unless otherwise stated. For example, the aspectsdescribed herein may also apply to heterodyne receivers or otherreceiver architectures.

The RF front-end 500 is configured to receive an incoming radio signal501. According to one embodiment, the radio signal 501 is a cellulartelephone signal, although other types of radio signals may be used invarious embodiments, as the aspects described herein relating to RFfront-ends are not limited to operation with cellular telephone signals.The radio signal 501 may include a carrier signal modulated with data(e.g., cellular telephone data) or may take any other suitable form.

The incoming radio signal 501 is received by the antenna 502 and passesthrough a band pass filter 504, which may be a duplexer. The resultingsignal is then amplified by a low noise amplifier (LNA) 506 anddown-converted by mixing the incoming radio signal with a referencesignal 512 using mixer 508. The reference signal 512 is illustrated inthis non-limiting example as having a frequency of 900 MHz for purposesof illustration, but may have any suitable frequency. It may begenerated by a frequency synthesizer 530 (illustrated as a fractionalPLL in this non-limiting example) which receives the previouslydescribed oscillating output signal 304. As previously mentioned, theoscillating output signal 304 may, in some embodiments, have anarbitrary frequency, at least before any tuning signals are applied tothe oscillator 302 generating the oscillating output signal. Aftermixing the incoming radio signal 501 and the reference signal 512 usingmixer 508 the resulting down-converted signal may be low pass-filteredin filter 514 and then converted from an analog signal to a digitalsignal using ADC 516. The resulting digital signal may contain the dataor information of the radio signal 501 (e.g., cellular telephone data).The digitized signal produced by ADC 516 may then be input to thebaseband electronics 518 for further processing. The basebandelectronics 518 may comprise a digital signal processor (DSP) 520, whichmay filter and condition the received data, e.g., the cellular telephonedata in those embodiments in which the RF front-end 500 is part of acellular telephone.

The accuracy with which the data of radio signal 501 is recovered maydepend, at least in part, on whether reference signal 512 has thedesired reference frequency (e.g., 900 MHz in this non-limitingexample). If the reference signal 512 does not have the desiredreference frequency, the data of radio signal 501 may not be accuratelyrecovered. According to some embodiments, it may be desirable for thereference signal 512 to have a frequency substantially matching thecarrier frequency of radio signal 501 plus some offset, e.g., 900 MHzmay correspond to the carrier frequency of the radio signal 501 plussome offset.

In the non-limiting example of FIG. 5, the reference signal 512 issynthesized by the frequency synthesizer 530, which again is afractional N PLL in this non-limiting example, although it should beappreciated that other types of frequency synthesizers may alternativelybe employed. The baseband electronics may adjust the frequencysynthesizer by applying a control signal 542 from output port 540(labeled “div_c”) to an input port 534 (labeled as “div_ctrl”), whichmay adjust a setting of the fractional N PLL. This may be done to adjustthe frequency of the reference signal 512 to match the carrier frequencyof the radio signal 501 when the frequency channel of the apparatus 500is changed, for example as occurs in cellular telephones when changingfrequency channels. The baseband electronics may therefore storeinformation indicating what setting of the N PLL corresponds to whatfrequency channel, so that the correct setting may be applied viacontrol signal 542.

To accurately recover the data of radio signal 501, the frequencysynthesizer 530 may be set to generate the reference signal 512 suchthat its frequency is as close to the carrier frequency of radio signal501 as possible. However, due to the finite step size of the fractionalN PLL and the fact that, in this non-limiting example, the frequencyprovided by oscillator 302 may be arbitrary, an offset Δf between thecarrier frequency of radio signal 501 and the frequency of referencesignal 512 may result. The baseband electronics may apply previouslydescribed tuning signals 308 and 314 to tune the oscillator 302 so thatthe frequency of oscillating output signal 304 facilitates generation byfrequency synthesizer 530 of a reference signal 512 having the desiredcarrier frequency. The values of tuning signals 308 and 314 may bedetermined by the baseband electronics in any of the manners previouslydescribed with respect to FIGS. 3 and 4, or in any other suitablemanner. The offset Δf may, in some embodiments, be in the range of ±50ppm to ±100 ppm, and therefore the desired carrier frequency may not beachievable with conventional RF front-ends. However, use of thefrequency steering tuning signal 308 in combination with the AFC tuningsignal 314 may allow the RF front-end to achieve accurate operation byenabling the reference signal 512 to have the desired target frequency.

It should be appreciated that the tuning functionality described withrespect to FIG. 5 may reduce or eliminate the occurrence of electricalinterference found in conventional RF front-ends, thus beneficiallyimproving the operation of the RF front-end. Conventional RF front-endsmay experience interference when the oscillator output signal orfrequency synthesizer signal, or some higher harmonics of those signals,undesirably mix with the received radio signal or higher harmonics ofthe received radio signal. According to the techniques described herein,for example in the non-limiting context of FIG. 5, the tuning range ofthe oscillator 302 may exceed the frequency step size of the frequencysynthesizer by a factor of two, such that there are two or more possiblesettings of the frequency synthesizer for any desired target frequencyof reference signal 512 based on an output signal of the oscillatorhaving a given frequency. Accordingly, there may be two or more suitablevalues for the frequency steering tuning signal which may be applied tothe oscillator 302 for any given desired target frequency of referencesignal 512, one corresponding to each of the two or more possiblefrequency synthesizer settings. Thus, if a particular frequency steeringvalue would result in undesirable electrical interference, one of theother possible frequency steering values for achieving the desiredreference signal 512 may be used to reduce or eliminate theinterference.

It should be appreciated from the foregoing that various aspects of thepresent invention are directed to systems and methods for generating areference signal having a target frequency upon receipt of anoscillating output signal having an arbitrary frequency. As previouslymentioned, various aspects of the present invention are alternativelydirected to systems and methods which operate upon an oscillating signalhaving an arbitrary frequency, and need not necessarily generate fromthe arbitrary frequency an oscillating signal having a desired targetfrequency (e.g., a standard oscillator frequency). For example, theconfiguration and/or operation of one or more components of a systemreceiving an oscillating signal having an arbitrary frequency may beadapted to permit operation of the system with the arbitrary frequency.Accordingly, the types of adaptations which may be implemented maydepend upon the components and configuration of the system receiving theoscillating signal from the oscillator. Various non-limiting examplesare now described, although it should be appreciated that otherimplementations are possible depending on the configuration andcomponents of the system.

According to one aspect of the present invention, a system receiving anoscillating signal having an arbitrary frequency includes an ADCconfigured to digitize a signal resulting from mixing a first signalwith the oscillating signal of arbitrary frequency, and the samplingrate of the ADC may be selected to account for such mixing. An exampleis given with respect to FIG. 6, which illustrates an RF front-end 600that is similar in many respects to previously described RF front-end500 of FIG. 5, and which uses identical reference numbers for thosecomponents that are the same as in FIG. 5.

As shown and previously described, an incoming radio signal 501 receivedon antenna 502 is down-converted in mixer 508 using a reference signal.The resulting down-converted signal is supplied to a filter and is thendigitized using an ADC. In the context of FIG. 5, the oscillator 302 andfrequency synthesizer 530 may be controlled by signals 542, 308, and 304to produce a reference signal 512 having a desired target frequency(illustrated as 900 MHz in the non-limiting example of FIG. 5), despitethe oscillator 302 initially being configured to produce an oscillatingsignal of arbitrary frequency (illustrated as 25.97425 MHz in FIG. 5).The desired target frequency for reference signal 512 may match thefrequency of the carrier signal of radio signal 501 including an offsetcorresponding to the intermediate frequency. In those instances, thedata of the down-converted signal output by mixer 508 may typicallyappear in the frequency domain at either the baseband frequency or anintermediate frequency. In such instances, the sampling rate of the ADC516 may be selected to suitably sample the down-converted signal suchthat the data on the down-converted signal is accurately captured by thedigitizing process implemented by ADC 516 without inducing a frequencyshift of the data during the digitizing process.

However, while it was previously described that apparatus 500 mayoperate by generating a reference signal 512 having a desired targetfrequency, such is not the case according to the present aspectdescribed with respect to RF front-end 600 of FIG. 6. According to thepresent aspect, oscillator 602 may be configured to generate anoscillating output signal 304 having an arbitrary frequency (e.g.,25.97425 MHz) which is not compensated by a frequency steering signal,such that the reference signal 612 does not have the desired targetfrequency (e.g., a frequency corresponding substantially to the carrierfrequency of radio signal 501 including an offset, corresponding to theintermediate frequency). For example, the tuning signal 308 may not beapplied according to this aspect, such that the arbitrary frequency ofoscillating output signal 304 results in reference signal 612 having afrequency differing from the desired target frequency. In thenon-limiting example of FIG. 6, the reference signal may have afrequency of, for example, 879.956 MHz, differing from a targetfrequency value of 880 MHz. As a result, the data of the down-convertedsignal output by mixer 508 is shifted in the frequency domain relativeto the intermediate frequency of the down-converted signal. Thedown-converted signal may then be filtered in a band-pass filter 614.Due to the frequency shift of the data of the down-converted signalrelative to the intermediate frequency, operating the ADC 616 at asampling rate as though the reference signal 612 had the desired targetfrequency (e.g., 880 MHz) results in the data of the digitized signalbeing frequency shifted relative to the intermediate frequency.

Thus, according to one aspect of the present invention, the samplingrate of the ADC 616 may be selected to compensate for the shift in thefrequency domain of the data of the down-converted signal relative tothe intermediate frequency. The sampling rate may be selected based on aknown or detected offset of the frequency of the reference signal 612from the carrier signal of radio signal 501 including the offset relatedto the intermediate frequency. For example, the frequency offset may beknown by receiving a value from memory 313, and the baseband electronicsmay then set a suitable sampling rate of the ADC 616, as a non-limitingexample. Other methods of determining a suitable sampling rate of theADC are also possible. In this manner, the RF front-end 600 may suitablyoperate to accurately recover the data of radio signal 501 despite theoscillator 602 providing an oscillating signal 304 having an arbitraryfrequency, and despite the frequency synthesizer 530 generating asynthesized signal having a frequency differing from the carrierfrequency of radio signal 501 including an offset corresponding to theintermediate frequency. Thus, the need for an oscillator providing aprecise frequency matching a standard oscillator frequency may beminimized or eliminated, which may simplify design of the system andallow for use of oscillators having various beneficial characteristics,such as ease of manufacture, low cost, or other beneficialcharacteristics.

According to one embodiment of the present aspect, the sampling rate ofthe ADC may be selected to match the resulting intermediate frequencygenerated by mixing of the radio signal 501 with the reference signal612 of arbitrary frequency. A non-limiting example is now given. Forpurposes of this non-limiting example, the intermediate frequency whichwould be generated by mixing the radio signal 501 with a referencesignal of 880 MHz may be 20 MHz. However, if the reference signal (e.g.,reference signal 612) instead is offset from 880 MHz by 50 ppm, theresulting intermediate frequency output by mixer 508 may be 20.044 MHz,rather than 20 MHz, in those embodiments in which the reference signalis 50 ppm lower than 880 MHz. Accordingly, the sampling rate of ADC 616may be selected to be approximately equal to the intermediate frequency,i.e., 20.044 MHz in this non-limiting example. It should be appreciatedthat operating the ADC 616 at such a frequency in this context is belowthe Nyquist criterion, such that the ADC 616 may effectively operate asa mixer, compensating for the offset from 880 MHz of the referencesignal 612. Again, it should be appreciated that this is merely onenon-limiting example. It should also be appreciated from the foregoingexample that the amount by which the sampling rate of ADC 616 may befrequency shifted compared to what would be appropriate if the referencesignal 612 had the desired target frequency may equal the absoluteoffset of the reference signal from the desired target frequency. Itshould also be appreciated that if the reference oscillator is lowerthan a desired target frequency, the sampling rate of the ADC 616 may beselected to be higher than if the reference oscillator had the desiredtarget frequency, and vice versa.

While the present aspect has been described with respect to the receivepath of the RF front-end 600, it should be appreciated that the sameconcept may apply equally well to the transmit path 622, although thatpath is not illustrated in detail in FIG. 6. For example, the transmitpath may include a digital-to-analog converter (DAC) configured toreceive a digital signal from DSP 520 including digital data to betransmitted. The DAC may convert the digital signal to an analog signal,which may then be up-converted by mixing with a suitable oscillatingreference signal (e.g., similar to reference signal 612). If theoscillating reference signal used for the up-conversion differs from astandard oscillator frequency, the data of the resulting up-convertedsignal may be shifted in the frequency domain relative to theintermediate frequency. Such a shift may be undesirable, and may beaccounted for in some embodiments by sampling the digital data signalfrom the DSP using a suitable sampling rate of the DAC to account forthe frequency shift which is induced during the up-conversion processusing the arbitrary frequency reference signal. According to oneembodiment, the sampling rate of the DAC may be selected toapproximately match the frequency shift of the intermediate frequencyintroduced during up-conversion, in a manner analogous to that justdescribed for the receive path. However, it should be appreciated thataccording to one embodiment if the arbitrary frequency of theoscillating reference signal used in the up-conversion process isgreater than the expected standard oscillator frequency, then thesampling rate of the DAC may be lowered compared to what would beappropriate if the oscillating reference signal had the standardoscillator frequency, and vice versa.

According to another aspect of the present invention, a system receivingan oscillating signal from an oscillator having an arbitrary frequencyincludes a digital signal processor (DSP) which may be used to digitallyshift data of a signal resulting from mixing a first signal (e.g., acellular telephone signal) with the oscillating signal of arbitraryfrequency. An example is now given with reference to FIG. 7, although itshould be appreciated that other systems may similarly implement thedescribed system and techniques. The RF front-end 700 of FIG. 7 issimilar in many respects to RF front-end 500, and the same referencenumbers are used to illustrate identical components.

As described, the RF front-end 700 may produce a down-converted signalfrom mixer 508, which may be low-pass filtered by filter 514 and thendigitized by ADC 516. The reference signal 712 used for the mixingprocess may not have a frequency substantially matching the frequency ofthe carrier signal of radio signal 501, such that the data of thedown-converted signal provided by mixer 508 may be shifted in thefrequency domain relative to the intermediate frequency, as previouslydescribed. For example, the reference signal 712 may have a frequency of900.045 MHz according to one embodiment, being offset from a targetvalue of 900 MHz due to oscillator 602 producing an oscillating outputsignal of arbitrary frequency. According to the previous aspect, thesampling rate of the ADC (e.g., ADC 616 in FIG. 6) may be shifted toaccount for the shift in the frequency domain of the data of thedown-converted signal. However, in the present aspect illustrated byFIG. 7, the sampling rate of the ADC 516 may be selected as if thereference signal 712 had a frequency matching that of the carrier signalof radio signal 501 (e.g., a target value of 900 MHz). As a result, thedigital signal provided by ADC 516 may include digital data shifted inthe frequency domain relative to the intermediate frequency. Accordingto the present aspect, the DSP 720 may receive the digital signal fromADC 516 and may re-sample the digital signal at a sampling rate suitableto effectively shift the digital data of the digital signal such that itaccurately represents the data of radio signal 501. According to thisaspect, the DSP may effectively operate as a frequency mixer.

While the present aspect has been described with respect to the receivepath of the RF front-end 700, it should be appreciated that the sameconcept may apply equally well to the transmit path 722, although thatpath is not illustrated in detail in FIG. 7. The transmit path 722 of RFfront-end 700 may be similar to the illustrated receive path of FIG. 7,although the output of the DSP may be provided to a DAC, which may thenbe coupled to a mixer to perform up-conversion of the signal to betransmitted. As previously described with respect to the aspectsrelating to altering a sampling rate of a DAC to account for use of anoscillating reference signal of arbitrary frequency, the up-conversionprocess performed using the oscillating signal of arbitrary frequencymay result in the data of the up-converted signal being shifted in thefrequency domain relative to the baseband and intermediate frequencies.In some embodiments, such a frequency shift of the data may beundesirable, and may be accounted for by digitally shifting the digitaldata of the digital data signal output by the DSP. The frequency shiftof the digital data may be induced by the DSP itself, according to onenon-limiting embodiment. The amount of the frequency shift induced bythe DSP may be selected to account for an expected frequency shift fromthe baseband and intermediate frequencies induced during up-conversionby the use of a reference signal of arbitrary frequency, and thereforein some embodiments may be selected based on a known value of thearbitrary frequency (e.g., provided from the oscillator as previouslydescribed). According to one embodiment, the DSP may shift the digitaldata to a lower frequency than would otherwise be used if the arbitraryfrequency of the oscillating reference signal used for up-conversion ishigher than the expected standard oscillator frequency. Similarly, theDSP may shift the digital data to a higher frequency than wouldotherwise be used if the arbitrary frequency of the oscillatingreference signal used for up-conversion is lower than the expectedstandard oscillator frequency. By suitable selection of the amount offrequency shift to induce in the digital data signal, the subsequent DACconversion and up-conversion using an oscillating reference signal ofarbitrary frequency may result in the data of the up-converted signalappearing at a desired frequency or frequencies.

According to a further aspect of the present invention, a systemreceiving an oscillating signal having an arbitrary frequency mayinclude a carrier tracking loop adapted to account for the arbitraryfrequency of the oscillating signal. Reference is made to FIG. 8 forpurposes of providing a non-limiting example. The reference signal 812has a frequency that does not substantially match the frequency of thecarrier signal of radio signal 501, and in this non-limiting example hasa frequency of approximately 880.044 MHz, arising from the arbitraryfrequency of the oscillating signal provided by oscillator 802 (which,it should be noted, is not configured to receive either a frequencysteering signal or an AFC tuning signal). As a result, thedown-converted signal provided by mixer 808 has data that is shifted inthe frequency domain relative to the intermediate frequency. Theresulting down-converted signal is filtered by band-pass filter 810. Thesampling rate of the ADC 814 in this non-limiting aspect is selected asthough the reference signal 812 has a frequency matching the frequencyof the carrier signal of radio signal 501 including the offsetequivalent to the intermediate frequency, such that the digital signalprovided by ADC 814 includes digital data shifted in the frequencydomain.

According to this aspect, a carrier tracking loop 815 is used at theintermediate frequency to lock to the carrier of the radio signal 501 atthe intermediate frequency. For this purpose the digital intermediatefrequency data is down-converted by a mixer 816 using a frequency from anumerically controlled oscillator (NCO) 822. The down-converted signalundergoes an integrate and dump 824 operation and is passed on to thereceiver processor 826. The receiver processor includes a PLLdiscriminator and loop filter and controls the NCO 822. In this manner,the digital data of the signal output by ADC 814 is effectivelydown-converted to the baseband such that it accurately reflects the dataof radio signal 501 independent of the frequency of the referenceoscillator 802. As a result the reference oscillator 802 does notrequire a AFC to obtain lock to the carrier frequency of the receivedradio signal 501.

As mentioned, it should be appreciated that the foregoing aspectsdescribed with respect to systems and methods for operating upon anoscillating signal having an arbitrary frequency are merely non-limitingexamples. Other systems and manners of adapting the configuration and/oroperation of the components of the system may be implemented.

Furthermore, while the foregoing aspects have been described in thecontext of cellular telephones, it should be appreciated that they arenot limited to such applications. For example, one or more of theaspects may apply to other types of communications systems (e.g., otherwireless communications systems, WiFi systems, etc.), as well as toother systems which make use of an oscillating reference signal providedby an oscillator including a mechanical resonator, such as navigationreceivers (e.g., GPS receivers), FM receivers, storage systems (e.g.,Fibre storage systems, including those using a reference oscillator togenerate or operate on an optical signal, etc.), video systems, wirelessinfrastructure (e.g., WiMax), networking systems (e.g., SPI-4, PCIExpress, etc.) or other devices. Thus, it should be appreciated that theforegoing discussion is provided for purposes of illustration, and isnot limiting.

Furthermore, it should be appreciated that the various aspects describedherein may be used with oscillators and systems designed to provide andoperate with any frequency of interest, and that the reference made to26 MHz in describing various aspects is not limiting, but rather is usedfor purposes of illustration. For example, the aspects described hereinmay be used to generate oscillating signals having standard oscillatorfrequencies of 12 MHz, 12.6 MHz, 13 MHz, 14.4 MHz, 16 MHz, 16.368 MHz,16.9 MHz, 19.2 MHz, 19.8 MHz, 20 MHz, 23.104 MHz, 24 MHz, 24.554 MHz, 26MHz, 27 MHz, 27.456 MHz, 32 MHz, 33.6 MHz, 38.4 MHz, 52 MHz, 669.3266MHz, any other standard oscillator frequency, or any other frequency orfrequencies of interest.

It should be appreciated from the foregoing that various benefits may beattained by application of one or more of the described aspects. Forexample, manufacturing constraints of conventional quartz crystalresonators may be relaxed since such resonators need not provide aprecise frequency matching a standard oscillator frequency to operateaccording to the various aspects described herein. Furthermore,resonator technologies other than conventional quartz crystal resonatorsmay be used even if they are not easily manufactured to provide aprecise output frequency matching a standard oscillator frequency. Thus,for example, MEMS resonators having output signal frequencies which maybe manufactured to a precision of ±10,000 ppm may be used. Suchresonators may provide beneficial characteristics in terms of signalnoise (e.g., phase noise among others), reduced spurious modes, improvednoise floor, jitter, ruggedness, cost, lower power consumption, andlighter weight, as well as other characteristics.

It should be appreciated that the various aspects of the inventiondescribed herein are not limited to use with oscillators employing anyparticular resonator technology. For example, the various aspectsdescribed herein may apply to oscillators using quartz crystalresonators, bulk acoustic wave (BAW) resonators, surface acoustic wave(SAW) resonators, plate acoustic wave (PAW) resonators, (thin) filmplate acoustic resonators (FPAR), film bulk acoustic resonators (FBAR),solid mounted resonators (SMR), contour mode resonators (CMR), thin-filmpiezoelectric on silicon (TPoS), microelectromechanical systems (MEMS)technology, or any other type of resonator technology that usesmechanical vibrations in a solid to excite a resonance frequency and usethis as a frequency reference in the oscillator. It should beappreciated that as used herein the term “mechanical resonator”encompasses at least quartz crystal resonators, BAW, SAW, PAW, SMR,FPAR, FBAR, CMR, thin-film piezoelectric on silicon (TPoS) resonatortechnology, and MEMS resonators. According to some embodiments, theoscillator may include a mechanical resonator comprising or formed ofone or more of the following materials: Quartz, Langasite, Silicon,Silicon oxide, Aluminum Nitride, Lithium Tantalate, Lithium Niobate,Zinc oxide, Gallium Arsenide, Cadmium Sulfide, Germanium. Otherresonator technologies may also be used.

Having thus described several aspects of at least one embodiment of thetechnology, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those skilled inthe art. Such alterations, modifications, and improvements are intendedto be within the spirit and scope of the technology. Accordingly, theforegoing description and drawings provide non-limiting examples only.

1. A method comprising: downconverting a cellular telephone signal, thecellular telephone signal modulated with data, using an oscillatingreference signal having an arbitrary frequency to generate adownconverted signal including the data; and sampling the downconvertedsignal with an analog-to-digital converter (ADC) using a sampling rateselected to induce a shift of the data of the downconverted signal in afrequency domain.
 2. The method of claim 1, wherein the arbitraryfrequency differs from a standard oscillator frequency by betweenapproximately 5,000 parts per million (ppm) and approximately 10,000ppm.
 3. The method of claim 1, further comprising receiving, from anoscillator having a mechanical resonator, the oscillating referencesignal having an arbitrary frequency.
 4. The method of claim 1, furthercomprising generating the oscillating reference signal from anoscillator output signal, wherein generating the oscillating referencesignal comprises receiving, from an oscillator having a mechanicalresonator, the oscillator output signal at a frequency synthesizer andsynthesizing the oscillating reference signal, wherein the oscillatingreference signal differs in frequency from a frequency of the oscillatoroutput signal.
 5. The method of claim 4, wherein the frequencysynthesizer is a phase-locked loop (PLL).
 6. The method of claim 1,further comprising receiving a value of the arbitrary frequency distinctfrom the oscillating reference signal and selecting the sampling rate ofthe ADC in response to receiving the value.
 7. A method comprising:generating a digital data signal having digital data; sampling thedigital data signal with a digital-to-analog converter (DAC) using asampling rate selected to induce a shift of the digital data in afrequency domain, the sampling resulting in an analog signal; andupconverting the analog signal using an oscillating reference signalhaving an arbitrary frequency to generate an upconverted signalincluding data corresponding to the digital data.
 8. A methodcomprising: downconverting a first signal, the first signal modulatedwith data, using an oscillating reference signal having an arbitraryfrequency to generate a downconverted signal including the data;sampling the downconverted signal with an analog-to-digital converter(ADC) to produce a digital signal including digital data correspondingto the data; and shifting, using a digital signal processor (DSP), thedigital data in a frequency domain.
 9. The method of claim 8, furthercomprising receiving the first signal modulated with data.
 10. Themethod of claim 8, further comprising receiving, from an oscillatorhaving a mechanical resonator, the oscillating reference signal havingan arbitrary frequency.
 11. The method of claim 8, further comprisinggenerating the oscillating reference signal from an oscillator outputsignal.
 12. The method of claim 11, wherein generating the oscillatingreference signal comprises receiving, from an oscillator having amechanical resonator, the oscillator output signal at a frequencysynthesizer and synthesizing the oscillating reference signal, whereinthe oscillating reference signal differs in frequency from a frequencyof the oscillator output signal.
 13. The method of claim 12, wherein thefrequency synthesizer is a phase-locked loop (PLL).
 14. The method ofclaim 8, wherein the first signal is a cellular telephone signal. 15.The method of claim 8, wherein the arbitrary frequency differs from astandard oscillator frequency by between approximately 500 parts permillion (ppm) and 2,000 ppm, and wherein sampling the downconvertedsignal with an ADC comprises using a sampling rate corresponding to thestandard oscillator frequency.
 16. A method comprising: generating adigital data signal having digital data; shifting the digital data in afrequency domain using a digital signal processor (DSP); sampling theshifted digital data with a digital-to-analog converter (DAC) to producean analog signal; and upconverting the analog signal using anoscillating reference signal having an arbitrary frequency to generatean upconverted signal including data corresponding to the digital data,wherein shifting the digital data in the frequency domain comprisesshifting the digital data by a frequency amount selected to account fora deviation of the arbitrary frequency from a standard oscillatorfrequency.
 17. A method comprising: downconverting a first signal, thefirst signal modulated with analog data, using an oscillating referencesignal having an arbitrary frequency to generate a downconverted signalincluding the analog data, the arbitrary frequency differing from astandard oscillator frequency; sampling the downconverted signal with ananalog-to-digital converter (ADC) to produce a digital signal includingdigital data corresponding to the analog data, the sampling beingperformed using a sampling rate corresponding to the standard oscillatorfrequency; and applying the digital signal to a carrier tracking loop.18. The method of claim 17, wherein the carrier tracking loop comprisesa numerically controlled oscillator (NCO) configured to digitally shiftthe digital data in a frequency domain.
 19. The method of claim 17,wherein the first signal is a cellular telephone signal modulated withcellular telephone data.
 20. The method of claim 17, wherein the firstsignal is a global positioning system (GPS) signal.